A year to the day after the Obama administration restored diplomatic ties with Cuba, the United States still doesn't have an ambassador officially representing it on the communist-led island.

And if Marco Rubio has his way, that’s not going to change anytime soon.

The Florida Republican, who decided to run for reelection to the Senate after his presidential bid failed, told POLITICO that he won’t drop his objections to any hypothetical ambassador nominee. And he scoffed at the notion that having an ambassador in Cuba could help the U.S. argue its case to the government there.

“A U.S. ambassador is not going to influence the Cuban government, which is a dictatorial, closed regime,” Rubio said in a phone interview earlier this week from Florida. He is leading in the polls in the Senate race there after reversing his decision to return to private life following his White House run.

A single senator can severely slow down the confirmation process for an ambassador. Rubio and Sens. Ted Cruz (R-Texas) and Robert Menendez (D-N.J.) are all harsh enough critics of the U.S. opening to Cuba that President Barack Obama has not even bothered to nominate an ambassador.

All three senators are of Cuban descent. They argue that the Cuban government, led by President Raúl Castro, brother of ailing revolutionary figure Fidel, will merely use its new relationship with Washington to cement its harsh rule.

The White House did not respond to a request for comment for this story; Obama, however, has noted in the past that the U.S. has a better chance of bringing about change in Cuba through engagement than isolation.